Re: [PATCH v4 5/6] KVM: MMU: combine guest pte read between walk and pte prefetch

Avi Kivity
2010-07-04T14:31:10Z

On 07/03/2010 04:03 PM, Xiao Guangrong wrote:
>
> Avi Kivity wrote:
>
>
>>>
>>> Well, in the description, it looked like everything was using small
>>> pages (in kvm, level=1 means PTE level, we need to change this one
>>> day). Please describe again and say exactly when the guest or host
>>> uses large pages.
>>>
>>>
>>>
>> Oh, I see what you mean.
>>
>> Regarding the patch, is it possible just to move the check before,
>> instead of adding the 'check' variable?
>>
>>
> Umm, if we move the check before the judgment, it'll check every level,
> actually, only the opened mapping and the laster level need checked, so
> for the performance reason, maybe it's better to keep two check-point.
>

What exactly are the conditions when you want to check?

Perhaps we do need to check every level. A write to a PDE (or higher
level) will clear the corresponding spte, but a fault immediately
afterwards can re-establish the spte to point to the new page.

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